The build plate

A plate is a build plate, not a file. It starts with one model and takes as many more as fit. Everything on it is sliced into one G-code file.

Adding models

Seven ways, all equivalent:

• Drag files onto the window
• The add model button in the tool cluster
• Add models at the bottom of the objects panel
• Open Model to Slice on the home screen
• Open with Cold Crabby, from anywhere else on the device — see below
• Reopening a recent plate, which brings all its models back
• Picking one from the library, where every model you have used is kept

Adding never clears what's already there. Only Empty Workplate does that.

Each new model is placed clear of the ones already on the bed, using the same spacing rules as Place objects, so a plate never opens with parts sitting inside each other. It arrives selected, ready to drag or turn.

Advanced — multi-part 3MF

A 3MF is a scene, not a model. Cold Crabby expands one into one object per build item, named from the file, all sharing the uploaded bytes. Duplicating an object shares them too — ten copies of a model cost one upload.

Opening a model from another app

On the desktop app and on iPhone/iPad, Cold Crabby registers itself as an app that opens .stl, .obj and .3mf — so a model can be sent straight to the plate without going through the file picker.

• Windows, macOS and Linux — double-click a model, or right-click it and choose Open with → Cold Crabby. If Cold Crabby is already running the model goes to the window you already have open, rather than starting a second one.
• iPhone and iPad — share a model to Cold Crabby from Shapr3D, Files, Mail or AirDrop, or long-press it in Files and choose Open With. In the share sheet the entry reads Copy to Cold Crabby.

A model opened this way always starts a fresh plate, whatever is on the bed already — it came from outside the app, so there is no arrangement on screen for it to join. To add a model to the plate you are already working on, drop it on the window or use Add models instead.

Advanced — making Cold Crabby the default

Cold Crabby registers as an alternate handler, so a machine that already has a slicer keeps it. To make Cold Crabby the one that opens on a double-click: on Windows, right-click a model → Open with → Choose another app → Always; on macOS, Get Info on a model → Open with → Change All.

What a plate remembers

A plate is saved as you work on it: its printer, filament and print profile, any settings you changed, and where each model sits. Reopening it — from the tab bar, from your history, or from a link — brings all of that back.

It remembers which profiles you picked, not a copy of them. So editing a print profile later reaches every plate using it, while the settings you changed on a particular plate stay as you left them. See Changes belong to the plate.

This survives closing the app. On the desktop app, the iPad and in the browser slicer, your models are kept on the device alongside the plate, so quitting — or iPadOS closing the app in the background to free memory — costs you nothing: reopen it, click the tab, and the plate comes back. Where the slicer runs on a server, the models are already there and the same is true from any device you sign in from.

When someone else is on the same plate

Where the slicer runs on a shared server, two people can have one plate open at once. If they save while you are looking at it — moving a model, changing a setting, adding a part — a small This workplate was changed elsewhere notice appears above the plate.

Nothing happens to your plate until you say so. Reload plate takes their version; Keep mine dismisses the notice and leaves you where you are, and whichever of you saves next is the version the plate keeps.

When a model can't come back

Models kept on the device are given a generous but finite amount of room. If you work through a great many large models, the ones you haven't opened in longest are eventually cleared to make space, and a plate that needed one tells you so when you open it. Add the model again and the plate is whole.

Moving things around

Pick a tool (or press its key), then drag the handles in the 3D view or type exact numbers into the card that appears underneath.

Tool	Key	Card gives you
Select & move	M	X / Y position in mm, Centre on bed, Drop to floor
Rotate	R	X / Y / Z in degrees, a 90° quarter turn per axis, Reset rotation
Scale	S	Per-axis or linked, as % or as a target size in mm, Reset scale
Pull to floor	F	Click any face to make it the bottom

Pull to floor is the fastest way to orient an awkward part: find the face that should sit on the bed, click it, done. No arithmetic about which axis to rotate.

Gravity (G) keeps objects resting on the bed after every move. It is on by default — a part left floating is not printable — and whichever way you set it is remembered for next time. Turn it off if you deliberately want something floating, for example when you're checking a support-free overhang.

You don't need the handles for a simple reposition. With a mouse, just drag a model across the bed — pressing one you haven't selected picks it up as you go. Dragging empty bed still turns the view. On a touch screen, tap a model first, then drag it: a finger crossing the plate to turn the view lands on models all the time, so nothing moves unless you picked it first.

For the last millimetre, the arrow keys nudge the selection 1 mm (Shift for 10, Alt/⌥ for 0.1). To lay a part on its side, the 90° buttons on the Rotate card turn it a quarter turn at a time.

Z zooms to the selection — or to everything when nothing is selected — and double-clicking a model does the same for that one.

Editing several objects at once

⌘-click (on a Mac) or Ctrl-click (elsewhere) adds or removes a model; Shift-click does too. ⌘/Ctrl + A takes all of them. To gather a group in one go, Shift-drag a box across them — anything the box touches is added — and Alt/⌥-drag a box to take some back out.

Without a keyboard, press and hold a model and choose Add to selection (or Remove from selection) — that also turns on Multi-select in the tool cluster, so every tap after it adds or removes one until you turn it off. With it on, the pencil can drag a selection box too.

Select more than one and the card keeps working:

• Position applies as an offset from the selection's shared centre, so the arrangement holds its shape instead of collapsing onto one coordinate.
• Rotation and scale apply to each object about its own centre.
• Size in mm measures each object separately, so a mixed batch all reaches the size you asked for.

The header names the tool you are holding — Move, Rotate, Scale — and adds the batch size for a multiple selection (Rotate · 3 objects). It doesn't name the object: every duplicate shares a filename, so that wouldn't tell you which.

Placing everything automatically

Place objects (A) lays the whole plate out in one go. Its card has:

• Auto-orient — turn each part onto a sensible face first. It looks for the largest face the part can actually rest on, and picks a different one only when that pose would leave a lot of the model hanging in the air or wouldn't fit under the gantry. A part that already arrived the right way up is left alone.
• Gap — how much room to leave between parts, in mm. It's measured between the parts themselves, not the boxes around them, so a curved or L-shaped part keeps the gap you asked for without reserving the empty corners it doesn't use. The same gap applies overhead, where one part passes above another.
• Preferred angle — shown read-only, because it belongs to the printer, not the plate. Many CoreXY machines print best at 45°. Change it in Settings → Printers. It's only applied when auto-orient runs.

Parts are nested by their real shape, and by how tall they are at each point. A plate prints a layer at a time, so the nozzle is always at the height of the tallest thing printed so far — which means one part can occupy the space above or below another as long as the two never want the same height in the same place. A part leaning at 45° hangs over its neighbour's roof; a small part tucks in under a flared rim. Parts also take a quarter turn where that helps them fit, and a plate with room to spare is gathered into one tight group in the middle rather than spread across it, which keeps the nozzle's hops between parts short.

Three things the app will not do, because the print would fail:

• Nothing is tucked under an overhang that needs support. Support material is as solid as the part above it, so a flat shelf keeps the whole column beneath it. Only an underside steep enough to print over thin air — by the same support angle the plate will be sliced with — frees the space below.
• No two parts lock together. Where one part passes over another, it passes over it everywhere they meet, so you can always lift the top one off first.
• Nothing overlaps at all when parts print one at a time. The print head drives past finished parts at full height, so sequential printing gives every part its own space from the plate up. The placement card says so when that's the mode you're in.

Anything that still doesn't fit is parked beside the plate rather than dropped, where the out-of-bounds warning picks it up.

This is one command, not two. There's no separate "orient everything" button that would fight with the arrangement.

Painting where support goes

Paint support (B) brushes support onto the model by hand, for the places the overhang rule gets wrong. Pressing B from the G-code preview switches back to the model for you.

• Enforce — put support here even if nothing overhangs enough to ask for it.
• Block — never put support here, however steep it gets.
• Erase — take painted marks back off.

Paint with a drag; the view stays still while you do, so a stroke can follow a curve. A pen with an eraser end (Surface Pen, Wacom) erases when you turn it over, whichever mode the brush is in. Press B again, or Esc, to put the brush down. Dragging from empty bed still turns the model, which is how you reach the other side without leaving the brush.

Size the brush by scrolling over the model — the ring under the pointer is its actual footprint. Zoom is still there on ⌘/Ctrl + scroll, and a trackpad pinch. Shift+B opens the mode and size controls at the pointer, so you don't have to travel back to the toolbar mid-stroke; the same two settings live on the tool's card as well, next to a count of what you've painted and a button to clear the plate.

Painting is independent of the overhang rule, and Support Auto (Process → Support) decides whether that rule runs at all. Leave it on and painting adds to what the slicer already found; turn it off and only what you paint gets support. Blockers apply either way.

Duplicating and deleting

Right-click a model — or press and hold it on a touch screen — for Duplicate, Drop to floor, Centre on bed, Zoom to and Remove, right where the model is. If you have several selected, the menu acts on all of them — the same menu whether you open it on the model or on its row in the objects panel.

Duplicate lays the copies beside the originals as a group and selects them, so they're ready to drag; ⌘/Ctrl + D again stamps another row. Centre on bed moves a selection as one piece, keeping how the parts sit relative to each other.

The objects panel has the same Duplicate and Remove as buttons on each row — there, Remove asks once before it takes effect.

Duplicates are cheap — they share the original's geometry.

Warnings

Two badges can appear on an object:

• Outside the build area — part of it is beyond the print volume. Checked against your printer's actual bed shape, not just a box.
• Overlaps another object — its footprint intersects another part's. Parts touching edge-to-edge don't count, so a tight auto-arrangement stays clean.

An object outside the build area also turns red on the plate, and goes back to its normal colour the moment you move it back on, so you can drag it into place without watching the panel.

Both are warnings. Slicing still runs — the check is an estimate and refusing would be more annoying than useful — but you should look before you print.

Naming and reopening plates

The plate's name is taken from the first model and can be edited in the title bar. The home screen lists recent plates with thumbnails; clicking one restores its models and layout.

Advanced — where a plate lives

In the browser, plate history is stored locally. On a self-hosted server it's kept server-side, so any machine on your network can reopen it. Uploaded model bytes are held per plate, which is how a plate with five files reopens with all five.

Exporting a plate as 3MF

Right-click (or long-press) the plate's tab, or an empty spot on the bed, and choose Export as 3MF…. Every model is saved where it sits on the plate, so the file reopens with the same layout here or in another slicer.

Advanced — what the file holds

Geometry and placement only. Slicer settings and painted support are not written. Copies made with Duplicate share one set of triangles in the file, so twenty copies cost little more than one.

Printing parts one at a time

Process → Objects → Print order offers two modes:

• By layer (default) — every part grows together, layer by layer.
• By object — each part is finished completely before the next starts, front to back.

By-object printing needs headroom: the gantry must clear everything already printed. Cold Crabby checks your printer's clearance height and radius and warns about parts that look too tall or too close together. It warns rather than refuses, because those clearances are estimates.

Whether the machine can cancel an individual object mid-print is a printer setting, not a process one — two printers can share a process but differ in firmware support. With it on, the G-code declares every part up front, so Mainsail, Fluidd and OctoPrint list them and let you cancel one that has failed while the rest of the plate carries on.